Long-chain neutral glycolipids and gangliosides of murine fibroblast lines and their low- and high-tumourigenic hybrids

Effect of plasma gangliosides on the growth of Ehrlich ascites tumor

Total plasma gangliosides of Ehrlich ascites tumor-bearing mice enhanced tumor growth when adoptively transferred with the same tumor cells in mice. However, individual gangliosides acted differently. Out of 6 gangliosides separated from plasma, 2 components enhanced tumor growth, whereas the remaining 4 inhibited tumor growth. Neither of the 2 enhancing components in various combinations with the 4 inhibitory components could restore the enhancing effect. The enhancing effect was restored only when both the enhancing components were mixed with the remaining 4 ganglioside components, i.e., with full/complete reconstitution.

Immunosuppressive activity of human neuroblastoma tumor gangliosides

Gangliosides are shed in substantial amounts by some tumors, including human neuroblastoma, and these molecules modulate experimental tumor formation in vivo. We now demonstrate that neuroblastoma tumor gangliosides have potent immunoregulatory activity. Gangliosides of every one of 17 tumors studied were highly inhibitory for the normal in vitro human lymphoproliferative responses to the soluble antigen, tetanus toxoid; 30 nmol ganglioside/ml caused 43% to greater than 99% inhibition and the mean concentration causing 50% inhibition was only 17.3 nmol/ml. Furthermore, gangliosides isolated from clinically more aggressive tumors (Stage III or IV) were up to twice as immunosuppressive as those of the generally less aggressive tumors (Stage I or II) (p less than 0.05). Taken together with the lack of immunosuppressive activity of normal plasma gangliosides, the potent activity of neuroblastoma gangliosides supports the hypothesis that one mechanism by which these shed molecules may act to enhance tumor formation in vivo is through abrogation of the host cellular immune response at the site of tumor formation.

Gangliosides shed by tumor cells enhance tumor formation in mice

The role of tumor cell membrane gangliosides in tumor formation was probed using a series of cloned murine AKR lymphoma cell lines. Tumor formation was directly related to high expression and shedding of membrane gangliosides. In vivo, as little as 1 pmol of purified total gangliosides of highly tumorigenic cells, injected intradermally with poorly tumorigenic cells (which lacked and did not shed gangliosides), markedly increased the tumorigenicity of these cells in syngeneic normal mice. Thus, gangliosides shed by tumor cells are a previously unrecognized, extremely potent enhancer of tumor formation in vivo.

Development of highly immunogenic variants of a rat fibrosarcoma line during in vitro cultivation

Rat fibrosarcoma KMT-17 cells decreased in tumorigenicity when cultured in vitro. Eight clones derived from cultured KMT-17 cell lines (c-KMT-17) were examined for their tumorigenicity, immunosensitivity, and immunogenicity. All the clones were less or nontumorigenic in normal syngeneic rats than KMT-17 cells maintained in vivo. All eight clones produced tumors in rats immunosuppressed with 600 rad 60Co; differences in degree of tumorigenicity were seen among clones in rats irradiated with 250 rad 60Co. Although immunosensitivity of the eight clones to complement-dependent and cell-mediated cytotoxicity was the same or less than that of KMT-17 cells, al leight clones induced greater transplantation resistance to KMT-17 than KMT-17 itself. Cold target inhibition tests demonstrated new antigens in a highly immunogenic variant in addition to the original tumor associated antigen (TAA). New glycolipids, not observed in KMT-17 cells, were demonstrated in the clones by thin layer chromatography. These results suggest that new antigens appearing during culture of KMT-17 may act as helper antigens for TAA, increasing the immunogenicity and decreasing the tumorigenicity of the cultured cells.

Carbohydrate structure in tumor immunity

Researchers have endeavored to define surface alterations associated with neoplasia for at least 25 years. In comparisons of normal tissues with animal and human tumors, cultured cells before and after transformation with oncogenic agents, tumorigenic and nontumorigenic transformed cells, metastatic and nonmetastatic tumor cells, high- and low-metastatic variants, and tumor cells before and after induction of differentiation to a less malignant phenotype, a consistent finding has been some form of alteration in surface carbohydrate structures. These changes in glycolipids, glycoproteins and glycosaminoglycans are reviewed, and their structures are illustrated. Both nucleotide sugar biosynthesis and glycosyltransferase changes have been associated with these alterations. In some cases, alterations in transformed cells were related to growth, rather than transformation. In others, the altered glycoconjugates are truly tumor-associated. There is evidence that cell surface glycoconjugates may function in growth control. Altered carbohydrate structures could also serve as receptors for growth promoting factors and be directly responsible for altered growth control. Recent studies with monoclonal antibodies indicate that the vast majority of antibodies recognizing tumor-associated antigens are detecting altered carbohydrate structures. Mechanisms by which the immune system can recognize these carbohydrate structures are considered, and immune recognition of tumor-associated carbohydrate structural alterations is explored. A number of these hypotheses relating to alterations in glycosylation, growth control, and tumor immunity deserve further investigation.

Differences of glycoconjugates exposed on hypernephroma and normal kidney cells

We analyzed the outer cell membranes of normal kidney cells, hypernephroma cells, nude mouse transplants of hypernephroma tissue, and cell lines derived from hypernephroma using horseradish peroxidase-coupled lectins of different specificity, in order to investigate their binding to cryostat sections or the cell surfaces of suspended single cells. We showed that hypernephroma cells express higher amounts of receptors for Robinia pseudoacacia lectin, soy bean lectin and Phaseolus vulgaris lectin compared to those prepared from normal kidneys. In contrast, Helix pomatia lectin is bound to connective tissue elements of both malignant and non-malignant tissue exclusively. L-fucose and D-galactose residues are detectable on malignant cells, but not on their non-malignant counterparts. However, the expression of the latter varies considerably among cells from different hypernephromas. No significant difference could be demonstrated between hypernephroma, hypernephroma cell lines and hypernephroma transplants in regard to the carbohydrate profile on the cell surfaces.

Monovalent antibodies directed to transformation-sensitive membrane components inhibit the process of viral transformation

Monovalent antibodies (Fab) directed to two classes of transformation-sensitive cell surface components, ganglioside and galactoprotein a (Gap a), inhibit the process of oncogenic viral transformation of cells. Mouse 3T3 cells infected with murine sarcoma virus were not transformed in terms of morphology change and enhancement of sugar uptake when the infected cells were cultured in the presence of monovalent antibodies directed to GM(1) ganglioside or to Gap a. Transformation inhibitory activity of these cell surface ligands was not related to cell growth inhibition because the monovalent antibodies to globoside and divalent Con A were growth inhibitory but did not inhibit oncogenic transformation. Neither anti-GM(1) Fab nor anti-Gap a Fab inhibited virus production. The transformation inhibitory activity of antiganglioside and anti-Gap a Fab was additionally assessed by inhibiting the transformed phenotype in NRK cell lines with mutants of avian sarcoma virus that are temperature sensitive for expression of the transformation phenotype (NRK/LA25). In this cell line, the GM(3) ganglioside (not GM(1)) and Gap a were transformation-sensitive cell surface components. The expression at permissive temperature of transformed phenotypes, such as morphology change and capability of growth in 0.3% agar, was inhibited by preincubation of the cells with anti-GM(3) Fab or anti-Gap a Fab.GM(3) labeling of NRK/LA25 cells decreased at permissive temperature, whereas preincubation of cells with anti-Gap a, which induces the inhibition of transformation after a temperature shift, prevented the decline of GM(3) label on the cell surface. The data suggest a possible correlation between GM(3) and Gap a expression. Application of monovalent antibodies to these transformation-sensitive components may prevent changes of these components on cell surfaces, and thus may result in abortion of phenotypic expression of transformation, although the transforming gene (src) has been set active. These results indicate that pericellular structures influence gene expression.

Chemical and immunological studies of cell surfaces from normal and transformed cells

Immunological and chemical studies of cell surfaces from normal and transformed BALB/c fibroblasts have shown alterations associated with transformation. The cells studied include normal lines which do not cause tumors when injected into BALB/c mice, viral transformants, and spontaneous transformants which cause tumors that either regress or grow progressively, killing the host. The spontaneously transformed progressors include cell lines which are immunogenic and nonimmunogenic as determined by the ability of tumor excision to protect an animal from subsequent rechallenge by tumor cells. Tumor-bearing mice produce lymphocytes which are nonspecifically cytotoxic for all the normal and transformed lines. Some of the cell lines induce specific antibody formation in BALB/hosts. Antisera have been prepared in rabbits which are specific for the transformed cell lines. These antisera can be used to determine specific surface changes on the transformed cells. Chemical studies have shown glycolipid alterations between the normal cells and some, but not all, of the transformants. Glycoproteins labeled by lactoperoxidase-125I or [3H] glucosamine were compared by SDS gel electrophoresis. Results from these studies do not show changes associated with malignancy. Individual glycoprotein regions from gels were treated with pronase, and the glycopeptides compared by Sephadex G50 chromatography. Alterations in glycopeptides from several cellular glycoproteins are the only changes which appear to be associated with malignancy.